1. Field of the Invention
The present invention concerns a board with cellular structure, which board comprises a core of cells located adjacent one another, which cells on at least one side are covered by a covering layer of panel in order to constitute a load bearing or supporting surface. Such board can be used as e.g. the load bearing surface of a pallet.
2. History of the Related Art
Pallets for storage and transport of goods must satisfy a plurality of requirements. They must be light, cheap to produce, possess great structural strength and rigidity against torque and in many cases be easy to clean and hygienic in other respects for e.g. transportation of foodstuffs.
Against this background the most usual pallets of wood have a series of drawbacks. The wood which is used must comply with many demands regarding freedom from damages, cracks, rot etc. and also have a definite moisture content during manufacture and moreover comply with severe demands on the strength of the nail joints and the like. This results in that pallets of wood become relatively complicated and expensive.
In the transport of and handling with foodstuffs, pallets of wood are unhygienic, as the wood attracts moisture and thereby causes mould. By the structure of the pallet many nooks are formed, within which dirt and germs may collect. Pallets of wood are also difficult to make and keep clean, which fact has contributed to attempts to manufacture pallets from some other, lighter, stronger and more hygienic material.
In order to eliminate the drawbacks inherent to pallets of wood one has, therefore, manufactured pallets of metal and various plastics, which proved to be deficient as to structural strength and usefulness. Attempts have been made to armour the plastic in various manners, for example by means of glass fibres or similar reinforcing materials.
This, however, involves disadvantages, because the reinforcing means make the pallet more expensive to manufacture and, in addition, increase the weight of the pallet. Another substantial problem arises also by the request that pallets of plastics after damages or wear shall be capable of becoming employed again, which is realized thereby that the pallet is ground down and re-cast. However, this treatment will be made difficult or impossible when pallets of armoured plastics are used, since the armour of glass fibres or similar material causes an unacceptable wear on the machines used for the grinding procedure.
Attempts have even been made to manufacture pallets with cellular structure for separate transports. Thus it is known from the Swedish published patent application 356,944 to manufacture a pallet from a light, cheap material such as paper, plastics or the like, wherein several separate casings of said material are disposed adjacent one another for constituting a pallet of honeycomb-like structure. The casings may herewith have cylindrical or angular shape and some casings are lengthened for serving as feet of the pallet.
There has been proposed also, e.g. according to U.S. Pat. Nos. 3,587,479, 3,709,161 and 4,319,530, to produce pallets of cardboard composed of cellular cavities, which are formed by assemblage of creased strips of cardboard.
These pallets with cellular structure have, as already mentioned, more the character of non-recurrent nature and are primarily intended for facilitating the handling by not being returned to the sender, which naturally limits the field of use, the pallet in these cases constituting part of the package of the goods.
The described pallets with cellular structure have, even if they should be produced for multiple use, several drawbacks. The structure with individual casings or assembled creased strips results in that the consumption of material becomes large and that a pallet of plastic material built up in this way and destined to endure multiple utilization obtains increased weight and, therefore, becomes expensive in manufacture and use. The application of cardboard as material for the pallet provokes, on the other hand, the same problems as wood material when the hygienic aspects are in consideration, for example. The known pallets for which cardboard or paper has been proposed as material, form due to their composition of a plurality of casings or creased layers a great number of cavities and/or nooks, within which dirt, germs etc. can accumulate.
The greatest disadvantage inherent to the pallets built up in accordance with the known art from individual casings or creased layers is, however, that they even with considerable dimensioning do not obtain nessecary strength for sustaining those strains which come up under the treatment of the pallet with or without load. Thus a strong spot load or impact against an edge or surface of the pallet will result in that the casings or cells are compressed and thereby given a permanent deformation which cannot be restored, since the wall material in the casings and possible covering layers has been cracked and cannot regain its original configuration. Therefore, as mentioned earlier, these pallets are best suited for single use and can in no way be compared with pallets of wood or cast, armoured plastics, which shall be usable repeatedly as pallets of exchange inspite of the rough treatment to which they often are subjected.